What happens to my blog when I graduate?

From Help Wiki

How to manage your Wordpress site after graduation

After you graduate, your site(s) at wordpress.evergreen.edu will be de-activated and deleted.

The de-activation process happens in mid-December, turning off any WordPress sites that do not have an active Evergreen login associated with them. The sites are then permanently deleted 3 months later at the beginning of Spring quarter.

Can I take it with me?

Yes. Export it. You can use the built-in export feature to export your site to WordPress.com or to other blogging/website creation services as well.

Another alternative to consider is to get your own domain name and host your own WordPress installation. Several web hosts provide pre-installed versions of WordPress and make it pretty easy to get up and running. With your own WordPress instance, you would be able to install any plugin or theme you wanted.

See: http://wordpress.org/hosting/ for a list of recommended hosts that provide easy WordPress hosting.